This application relates to an enclosure for regulating the temperature of one or more storage batteries.
Batteries are often used in remote locations where electrical power is needed to power lights, communication equipment, and other such devices requiring low level but relatively continuous power. Photovoltaic panels may be used to gather the electrical power when solar energy is available, and the energy stored for later use. Alternatively, generators may be used to generate substantial power during short intervals while the generators are operating, and the electrical energy stored in batteries for longer term use.
Remote batteries and their associated equipment may be exposed to temperature extremes ranging from desert summers where the temperature can reach well over 100 degrees Fahrenheit, to mountain winters where the temperature can plunge to well below Zero. While the equipment can be housed to protect it against rain and sand, such temperature extremes often cannot be avoided. In addition, the equipment is exposed to daily temperature cycles between afternoon highs and early morning lows.
Batteries, particularly the lead acid batteries which are typically used in such installations, are quite sensitive to ambient temperature. At temperatures above 77 degrees Fahrenheit, battery lifetime is substantially shortened. For example, a lead acid battery will age twice as fast at 93 degrees Fahrenheit, and four times as fast at 111 degrees Fahrenheit, as it will age at 77 degrees Fahrenheit. At 40 degrees Fahrenheit, it ages at 60% of the rate at 77 degrees Fahrenheit. Conversely, at colder temperatures, a lead acid battery has less electrical storage capacity, and if it is at a low state of charge, a battery may freeze at temperatures as high as 20 degrees Fahrenheit.
Daily temperature cycles also shorten battery life, especially in a solar energy application. Around midday, when solar energy is at its height, the batteries are often being charged at their maximum rate. Battery charging generates heat both through the exothermic reaction of the electrolyte, and the internal electrical resistance of the battery. This heating occurs at the warmest time of the day, and the temperature excursions of the battery often exceed the excursions in ambient temperature, further reducing battery lifetime.
In remote installations, batteries are typically stored in a metal box which is either directly exposed to the elements, or poorly sheltered. While this protects the batteries from rain and sand, it does little to minimize the temperature extremes imposed on the batteries and may actually aggravate such extremes because heat is trapped in the box. The battery box can be buried, but the value of burying the battery box may be limited. If the batteries are buried no more than 5 feet deep, ground temperature in a desert installation may actually exceed average summer air temperature. Deeper burial is often prohibitively expensive, and makes access and ventilation difficult. No effective solution is found in the prior art to limit both the temperature extremes and the temperature cycles encountered by batteries in remote installations.